R12 to R134 conversion on 86 with radial compressor issues

[demian5]

Help -

I have replaced the compressor 3 times in this truck along with the drier and orifice tube. The compressors keep locking up. I use the right amount (maybe a little more) of PAG oil. That gets about 8OZ into the system. I used reman compressors before, now I have a brand new compressor on it.

I charge until low side is at 30 psi at about 2000 rpm. BUT when it idles (600 rpm the kick up solenoid doesn't work), low side pressure goes to about 75 psi.

Any ideas? I had to plug the high side port because it was leaking.

I have flushed the system a few times with ac flush before replacing parts.

I ran the vacuum down to 30hg for an hour and it held steady for ever after shutting the pump off.

The new compressor is screeching here and there but its staying cold. It cycles of bause at about 3k rpm (cruising RPM) charge goes below 30 and the switch turns it off.

HELP!